A pressure vessel (also referred to herein as a storage tank, or more simply, a tank) for storing high pressure gaseous mediums (such as hydrogen, compressed natural gas, or air) typically includes one or more liners, at least one mouthpiece (typically in the form of a metal boss) and a filament wound outer shell reinforcement structure. The pressure vessel may be incorporated into a vehicle to supply fuel (for example, hydrogen) or an oxidant (such as oxygen) to a fuel cell stack capable of powering the vehicle.
The liner may be formed utilizing conventional methods such as rotational molding, blow molding, injection molding, or thermoforming with a plastic, typically from a thermoplastic, such as polyethylene, PET, polyoxymethylene (POM), ABS/PC, ethylene vinyl alcohol, or a nylon material, for example, by disposing penetrating elements in a die cavity with a polymer resin, heating the mold while being rotated to cause the polymer resin to melt and coat walls of the die cavity, cooling the die, and removing the molded liner.
The metal boss is typically configured with one of threads or other coupling means to accept a valve, sensor, coupler, conduit or other device used to provide a coupling point for the pressure vessel. The gaseous medium passes through the boss when one of entering and exiting the pressure vessel.
The wound outer shell—which normally provides the bulk of the support or reinforcement structure for the pressure vessel—is typically formed by a filament winding process, and is connected to the liner and cured in an autoclave.
Currently, the materials and known methods used to form the pressure vessel provide poor durability effects. For example, the liner generally cannot withstand stress forces such that the tank is exposed to over its operational life, such as those associated with being subjected to numerous filling and emptying cycles, as well as temperature extremes. Thus, in one form, a minimum pressure should be maintained in the tank at all times to ensure that the liner is firmly supported by the reinforcement structure. At pressures below the minimum pressure—for example less than about 20 bar—the liner and reinforcement structure may separate from each other causing a “loose” liner effect. If the pressurized fluid is introduced into the pressure vessel quickly under high pressure while the pressure within the tank is below the proscribed minimum, the liner will bump against the reinforcement structure very hard causing a “buckled” liner. The liner could rupture, allowing the contents to flow through the outer layer into the environment. In addition, pressurized fluid trapped in the gap between the liner and reinforcement structure can damage one or both of the liner and reinforcement structure. Significant temperature changes may produce the same deleterious effects.